Generally, a silicon source gas may be applied to a silicon substrate to grow silicon from the silicon substrate, thereby forming an epitaxial layer. Further, a silicon source gas and an etching gas may be applied to a silicon substrate to grow silicon from the silicon substrate and to etch the silicon on an insulating layer of the silicon substrate by the etching gas, thereby forming a selective epitaxial layer.
When the etching gas is not in its decomposed form in a reaction chamber, the epitaxial layer on the insulating layer may not be removed. In order to prevent the above-mentioned problem, a single type apparatus may perform an SEG process at a high temperature. In contrast, a batch type apparatus may require a great amount of the etching gas. In the batch type apparatus, the etching gas and the silicon source gas may not be applied simultaneously. As a result, the epitaxial layer on the silicon substrate may not have a uniform distribution.